Decoder, encoder and method for informed loudness estimation employing by-pass audio object signals in object-based audio coding systems

ABSTRACT

A decoder for generating an audio output signal having one or more audio output channels is provided, having a receiving interface for receiving an audio input signal having a plurality of audio object signals, for receiving loudness information on the audio object signals, and for receiving rendering information indicating whether one or more of the audio object signals shall be amplified or attenuated, further having a signal processor for generating the one or more audio output channels of the audio output signal, configured to determine a loudness compensation value depending on the loudness information and depending on the rendering information, and configured to generate the one or more audio output channels of the audio output signal from the audio input signal depending on the rendering information and depending on the loudness compensation value. One or more by-pass audio object signals are employed for generating the audio output signal. Moreover, an encoder is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/822,678 filed Aug. 10, 2015 which is a continuation ofInternational Application No. PCT/EP2014/075801, filed Nov. 27, 2014,which are incorporated herein by reference in their entirety, andadditionally claims priority from European Application No. 13194664.2,filed Nov. 27, 2013, which is also incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

The present invention relates to audio signal encoding, processing anddecoding, and, in particular, to a decoder, an encoder and method forinformed loudness estimation in object-based audio coding systems.

Recently, parametric techniques for bitrate-efficienttransmission/storage of audio scenes comprising multiple audio objectsignals have been proposed in the field of audio coding [BCC, JSC, SAOC,SAOC1, SAOC2] and informed source separation [ISS1, ISS2, ISS3, ISS4,ISS5, ISS6]. These techniques aim at reconstructing a desired outputaudio scene or audio source object based on additional side informationdescribing the transmitted/stored audio scene and/or source objects inthe audio scene. This reconstruction takes place in the decoder using aninformed source separation scheme. The reconstructed objects may becombined to produce the output audio scene. Depending on the way theobjects are combined, the perceptual loudness of the output scene mayvary.

In TV and radio broadcast, the volume levels of the audio tracks ofvarious programs may be normalized based on various aspects, such as thepeak signal level or the loudness level. Depending on the dynamicproperties of the signals, two signals with the same peak level may havea widely differing level of perceived loudness. Now switching betweenprograms or channels the differences in the signal loudness are veryannoying and have been to be a major source for end-user complaints inbroadcast.

In the known technology, it has been proposed to normalize all theprograms on all channels similarly to a common reference level using ameasure based on perceptual signal loudness. One such recommendation inEurope is the EBU Recommendation R128 [EBU] (later referred to as R128).

The recommendation says that the “program loudness”, e.g., the averageloudness over one program (or one commercial, or some other meaningfulprogram entity) should equal a specified level (with small alloweddeviations). When more and more broadcasters comply with thisrecommendation and the necessitated normalization, the differences inthe average loudness between programs and channels should be minimized.

Loudness estimation can be performed in several ways. There existseveral mathematical models for estimating the perceptual loudness of anaudio signal. The EBU recommendation R128 relies on the model presentedin ITU-R BS.1770 (later referred to as BS.1770) (see [ITU]) for theloudness estimation.

As stated before, e.g., according to the EBU Recommendation R128, theprogram loudness, e.g., the average loudness over one program shouldequal a specified level with small allowed deviations. However, thisleads to significant problems when audio rendering is conducted,unsolved until now in the known technology. Conducting audio renderingon the decoder side has a significant effect on the overall/totalloudness of the received audio input signal. However, despite scenerendering is conducted, the total loudness of the received audio signalshall remain the same.

Currently, no specific decoder-side solution exists for this problem.

EP 2 146 522 A1 ([EP]), relates to concepts for generating audio outputsignals using object based metadata. At least one audio output signal isgenerated representing a superposition of at least two different audioobject signals, but does not provide a solution for this problem.

WO 2008/035275 A2 ([BRE]) describes an audio system comprising anencoder which encodes audio objects in an encoding unit that generates adown-mix audio signal and parametric data representing the plurality ofaudio objects. The down-mix audio signal and parametric data istransmitted to a decoder which comprises a decoding unit which generatesapproximate replicas of the audio objects and a rendering unit whichgenerates an output signal from the audio objects. The decoderfurthermore contains a processor for generating encoding modificationdata which is sent to the encoder. The encoder then modifies theencoding of the audio objects, and in particular modifies the parametricdata, in response to the encoding modification data. The approach allowsmanipulation of the audio objects to be controlled by the decoder butperformed fully or partly by the encoder. Thus, the manipulation may beperformed on the actual independent audio objects rather than onapproximate replicas thereby providing improved performance.

EP 2 146 522 A1 ([SCH]) discloses an apparatus for generating at leastone audio output signal representing a superposition of at least twodifferent audio objects comprises a processor for processing an audioinput signal to provide an object representation of the audio inputsignal, where this object representation can be generated by aparametrically guided approximation of original objects using an objectdownmix signal. An object manipulator individually manipulates objectsusing audio object based metadata referring to the individual audioobjects to obtain manipulated audio objects. The manipulated audioobjects are mixed using an object mixer for finally obtaining an audiooutput signal having one or several channel signals depending on aspecific rendering setup.

WO 2008/046531 A1 ([ENG]) describes an audio object coder for generatingan encoded object signal using a plurality of audio objects includes adownmix information generator for generating downmix informationindicating a distribution of the plurality of audio objects into atleast two downmix channels, an audio object parameter generator forgenerating object parameters for the audio objects, and an outputinterface for generating the imported audio output signal using thedownmix information and the object parameters. An audio synthesizer usesthe downmix information for generating output data usable for creating aplurality of output channels of the predefined audio outputconfiguration.

It would be desirable to have an accurate estimate of the output averageloudness or the change in the average loudness without a delay and whenthe program does not change or the rendering scene is not changed, theaverage loudness estimate should also remain static.

SUMMARY

According to an embodiment, a decoder for generating an audio outputsignal having one or more audio output channels may have: a receivinginterface for receiving an audio input signal having a plurality ofaudio object signals, for receiving loudness information on the audioobject signals, and for receiving rendering information indicatingwhether one or more of the audio object signals shall be amplified orattenuated, and a signal processor for generating the one or more audiooutput channels of the audio output signal, wherein the receivinginterface is configured to receive a downmix signal having one or moredownmix channels as the audio input signal, wherein the one or moredownmix channels have the audio object signals, and wherein the numberof the one or more downmix channels is smaller than the number of theaudio object signals, wherein the receiving interface is configured toreceive downmix information indicating how the audio object signals aremixed within the one or more downmix channels, wherein the receivinginterface is configured to receive one or more further by-pass audioobject signals, wherein the one or more further by-pass audio objectsignals are not mixed within the downmix signal, wherein the receivinginterface is configured to receive the loudness information indicatinginformation on the loudness of the audio object signals which are mixedwithin the downmix signal and indicating information on the loudness ofthe one or more further by-pass audio object signals which are not mixedwithin the downmix signal, wherein the signal processor is configured todetermine a loudness compensation value depending on the information onthe loudness of the audio object signals which are mixed within thedownmix signal, and depending on the information on the loudness of theone or more further by-pass audio object signals which are not mixedwithin the downmix signal, and wherein the signal processor isconfigured to generate the one or more audio output channels of theaudio output signal from the audio input signal depending on the downmixinformation, depending on the rendering information and depending on theloudness compensation value.

According to another embodiment, an encoder may have: an object-basedencoding unit for encoding a plurality of audio object signals to obtainan encoded audio signal having the plurality of audio object signals,and an object loudness encoding unit for encoding loudness informationon the audio object signals, wherein the loudness information has one ormore loudness values, wherein each of the one or more loudness valuesdepends on one or more of the audio object signals, wherein theobject-based encoding unit is configured to receive the audio objectsignals, wherein each of the audio object signals is assigned to exactlyone of two or more groups, wherein each of the two or more groups hasone or more of the audio object signals, wherein the object-basedencoding unit is configured to downmix the audio object signals, beingcomprised by the two or more groups, to obtain a downmix signal havingone or more downmix audio channels as the encoded audio signal, whereinthe number of the one or more downmix channels is smaller than thenumber of the audio object signals being comprised by the two or moregroups, wherein the object loudness encoding unit is assigned to receiveone or more further by-pass audio object signals, wherein each of theone or more further by-pass audio object signals is assigned to a thirdgroup, wherein each of the one or more further by-pass audio objectsignals is not comprised by the first group and is not comprised by thesecond group, wherein the object-based encoding unit is configured tonot downmix the one or more further by-pass audio object signals withinthe downmix signal, and wherein the object loudness encoding unit isconfigured to determine a first loudness value, a second loudness valueand a third loudness value of the loudness information, the firstloudness value indicating a total loudness of the one or more audioobject signals of the first group, the second loudness value indicatinga total loudness of the one or more audio object signals of the secondgroup, and the third loudness value indicating a total loudness of theone or more further by-pass audio object signals of the third group, oris configured to determine a first loudness value and a second loudnessvalue of the loudness information, the first loudness value indicating atotal loudness of the one or more audio object signals of the firstgroup, and the second loudness value indicating a total loudness of theone or more audio object signals of the second group and of the one ormore further by-pass audio object signals of the third group.

According to still another embodiment, a system may have: an encoder asmentioned above for encoding a plurality of audio object signals toobtain an encoded audio signal having the plurality of audio objectsignals, and a decoder as mentioned above for generating an audio outputsignal having one or more audio output channels, wherein the decoder isconfigured to receive the encoded audio signal as an audio input signaland to receive the loudness information wherein the decoder isconfigured to further receive rendering information, wherein the decoderis configured to determine a loudness compensation value depending onthe loudness information and depending on the rendering information, andwherein the decoder is configured to generate the one or more audiooutput channels of the audio output signal from the audio input signaldepending on the rendering information and depending on the loudnesscompensation value.

According to another embodiment, a method for generating an audio outputsignal having one or more audio output channels may have the steps of:receiving an audio input signal having a plurality of audio objectsignals, receiving loudness information indicating information on theloudness of the audio object signals which are mixed within the downmixsignal and indicating information on the loudness of the one or morefurther by-pass audio object signals which are not mixed within thedownmix signal, and receiving rendering information indicating whetherone or more of the audio object signals shall be amplified orattenuated, receiving a downmix signal having one or more downmixchannels as the audio input signal, wherein the one or more downmixchannels have the audio object signals, and wherein the number of theone or more downmix channels is smaller than the number of the audioobject signals, receiving downmix information indicating how the audioobject signals are mixed within the one or more downmix channels,receiving one or more further by-pass audio object signals, wherein theone or more further by-pass audio object signals are not mixed withinthe downmix signal, determining a loudness compensation value dependingon the information on the loudness of the audio object signals which aremixed within the downmix signal, and depending on the information on theloudness of the one or more further by-pass audio object signals whichare not mixed within the downmix signal, and generating the one or moreaudio output channels of the audio output signal from the audio inputsignal depending on the downmix information, depending on the renderinginformation and depending on the loudness compensation value.

According to another embodiment, a method for encoding may have thesteps of: encoding an audio input signal having a plurality of audioobject signals, and encoding loudness information on the audio objectsignals, wherein the loudness information has one or more loudnessvalues, wherein each of the one or more loudness values depends on oneor more of the audio object signals, wherein each of the audio objectsignals is assigned to exactly one of two or more groups, wherein eachof the two or more groups has one or more of the audio object signals,wherein encoding the loudness information on the audio object signals isconducted by downmixing the audio object signals, being comprised by thetwo or more groups, to obtain a downmix signal having one or moredownmix audio channels as the encoded audio signal, wherein the numberof the one or more downmix channels is smaller than the number of theaudio object signals being comprised by the two or more groups, whereineach of one or more further by-pass audio object signals is assigned toa third group, wherein each of the one or more further by-pass audioobject signals is not comprised by the first group and is not comprisedby the second group, wherein encoding the loudness information on theaudio object signals is conducted by not downmixing the one or morefurther by-pass audio object signals within the downmix signal, andwherein encoding the loudness information on the audio object signals isconducted by determining a first loudness value, a second loudness valueand a third loudness value of the loudness information, the firstloudness value indicating a total loudness of the one or more audioobject signals of the first group, the second loudness value indicatinga total loudness of the one or more audio object signals of the secondgroup, and the third loudness value indicating a total loudness of theone or more further by-pass audio object signals of the third group, oris configured to determine a first loudness value and a second loudnessvalue of the loudness information, the first loudness value indicating atotal loudness of the one or more audio object signals of the firstgroup, and the second loudness value indicating a total loudness of theone or more audio object signals of the second group and of the one ormore further by-pass audio object signals of the third group.

Another embodiment may have a computer program for implementing theabove methods of decoding and encoding when being executed on a computeror signal processor.

An informed way for estimating the loudness of the output in anobject-based audio coding system is provided. The provided concepts relyon information on the loudness of the objects in the audio mixture to beprovided to the decoder. The decoder uses this information along withthe rendering information for estimating the loudness of the outputsignal. This allows then, for example, to estimate the loudnessdifference between the default downmix and the rendered output. It isthen possible to compensate for the difference to obtain approximatelyconstant loudness in the output regardless of the rendering information.The loudness estimation in the decoder takes place in a fully parametricmanner, and it is computationally very light and accurate in comparisonto signal-based loudness estimation concepts.

Concepts for obtaining information on the loudness of the specificoutput scene using purely parametric concepts are provided, which thenallows for loudness processing without explicit signal-based loudnessestimation in the decoder. Moreover, the specific technology of SpatialAudio Object Coding (SAOC) standardized by MPEG [SAOC] is described, butthe provided concepts can be used in conjunction with other audio objectcoding technologies, too.

A decoder for generating an audio output signal comprising one or moreaudio output channels is provided. The decoder comprises a receivinginterface for receiving an audio input signal comprising a plurality ofaudio object signals, for receiving loudness information on the audioobject signals, and for receiving rendering information indicatingwhether one or more of the audio object signals shall be amplified orattenuated. Moreover, the decoder comprises a signal processor forgenerating the one or more audio output channels of the audio outputsignal. The signal processor is configured to determine a loudnesscompensation value depending on the loudness information and dependingon the rendering information. Furthermore, the signal processor isconfigured to generate the one or more audio output channels of theaudio output signal from the audio input signal depending on therendering information and depending on the loudness compensation value.

According to an embodiment, the signal processor may be configured togenerate the one or more audio output channels of the audio outputsignal from the audio input signal depending on the renderinginformation and depending on the loudness compensation value, such thata loudness of the audio output signal is equal to a loudness of theaudio input signal, or such that the loudness of the audio output signalis closer to the loudness of the audio input signal than a loudness of amodified audio signal that would result from modifying the audio inputsignal by amplifying or attenuating the audio object signals of theaudio input signal according to the rendering information.

According to another embodiment, each of the audio object signals of theaudio input signal may be assigned to exactly one group of two or moregroups, wherein each of the two or more groups may comprise one or moreof the audio object signals of the audio input signal. In such anembodiment, the receiving interface may be configured to receive aloudness value for each group of the two or more groups as the loudnessinformation, wherein said loudness value indicates an original totalloudness of the one or more audio object signals of said group.Furthermore, the receiving interface may be configured to receive therendering information indicating for at least one group of the two ormore groups whether the one or more audio object signals of said groupshall be amplified or attenuated by indicating a modified total loudnessof the one or more audio object signals of said group. Moreover, in suchan embodiment, the signal processor may be configured to determine theloudness compensation value depending on the modified total loudness ofeach of said at least one group of the two or more groups and dependingon the original total loudness of each of the two or more groups.Furthermore, the signal processor may be configured to generate the oneor more audio output channels of the audio output signal from the audioinput signal depending on the modified total loudness of each of said atleast one group of the two or more groups and depending on the loudnesscompensation value.

In particular embodiments, at least one group of the two or more groupsmay comprise two or more of the audio object signals.

Moreover an encoder is provided. The encoder comprises an object-basedencoding unit for encoding a plurality of audio object signals to obtainan encoded audio signal comprising the plurality of audio objectsignals. Furthermore, the encoder comprises an object loudness encodingunit for encoding loudness information on the audio object signals. Theloudness information comprises one or more loudness values, wherein eachof the one or more loudness values depends on one or more of the audioobject signals.

According to an embodiment, each of the audio object signals of theencoded audio signal may be assigned to exactly one group of two or moregroups, wherein each of the two or more groups comprises one or more ofthe audio object signals of the encoded audio signal. The objectloudness encoding unit may be configured to determine the one or moreloudness values of the loudness information by determining a loudnessvalue for each group of the two or more groups, wherein said loudnessvalue of said group indicates an original total loudness of the one ormore audio object signals of said group.

Furthermore, a system is provided. The system comprises an encoderaccording to one of the above-described embodiments for encoding aplurality of audio object signals to obtain an encoded audio signalcomprising the plurality of audio object signals, and for encodingloudness information on the audio object signals. Moreover, the systemcomprises a decoder according to one of the above-described embodimentsfor generating an audio output signal comprising one or more audiooutput channels. The decoder is configured to receive the encoded audiosignal as an audio input signal and the loudness information. Moreover,the decoder is configured to further receive rendering information.Furthermore, the decoder is configured to determine a loudnesscompensation value depending on the loudness information and dependingon the rendering information. Moreover, the decoder is configured togenerate the one or more audio output channels of the audio outputsignal from the audio input signal depending on the renderinginformation and depending on the loudness compensation value.

Moreover, a method for generating an audio output signal comprising oneor more audio output channels is provided. The method comprises:

-   -   Receiving an audio input signal comprising a plurality of audio        object signals.    -   Receiving loudness information on the audio object signals.    -   Receiving rendering information indicating whether one or more        of the audio object signals shall be amplified or attenuated.    -   Determining a loudness compensation value depending on the        loudness information and depending on the rendering information.        And:    -   Generating the one or more audio output channels of the audio        output signal from the audio input signal depending on the        rendering information and depending on the loudness compensation        value.

Furthermore, a method for encoding is provided. The method comprises:

-   -   Encoding an audio input signal comprising a plurality of audio        object signals. And:    -   Encoding loudness information on the audio object signals,        wherein the loudness information comprises one or more loudness        values, wherein each of the one or more loudness values depends        on one or more of the audio object signals.

Moreover, a computer program for implementing the above-described methodwhen being executed on a computer or signal processor is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present invention are described inmore detail with reference to the figures, in which:

FIG. 1 illustrates a decoder for generating an audio output signalcomprising one or more audio output channels according to an embodiment,

FIG. 2 illustrates an encoder according to an embodiment,

FIG. 3 illustrates a system according to an embodiment,

FIG. 4 illustrates a Spatial Audio Object Coding system comprising anSAOC encoder and a SAOC decoder,

FIG. 5 illustrates an SAOC decoder comprising a side informationdecoder, an object separator and a renderer,

FIG. 6 illustrates a behavior of output signal loudness estimates on aloudness change,

FIG. 7 depicts informed loudness estimation according to an embodiment,illustrating components of an encoder and a decoder according to anembodiment,

FIG. 8 illustrates an encoder according to another embodiment,

FIG. 9 illustrates an encoder and a decoder according to an embodimentrelated to the SAOC-Dialog Enhancement, which comprises bypass channels,

FIG. 10 depicts a first illustration of a measured loudness change andthe result of using the provided concepts for estimating the change inthe loudness in a parametrical manner,

FIG. 11 depicts a second illustration of a measured loudness change andthe result of using the provided concepts for estimating the change inthe loudness in a parametrical manner, and

FIG. 12 illustrates another embodiment for conducting loudnesscompensation.

DETAILED DESCRIPTION OF THE INVENTION

Before embodiments are described in detail, loudness estimation, SpatialAudio Object Coding (SAOC) and Dialogue Enhancement (DE) are described.

At first, loudness estimation is described.

As already stated before, the EBU recommendation R128 relies on themodel presented in ITU-R BS.1770 for the loudness estimation. Thismeasure will be used as an example, but the described concepts below canbe applied also for other loudness measures.

The operation of the loudness estimation according to BS.1770 isrelatively simple and it is based on the following main steps [ITU]:

-   -   The input signal x_(i) (or signals in the case of multi-channel        signal) is filtered with a K-filter (a combination of a shelving        and a high-pass filters) to obtain the signal(s) y_(i).    -   The mean squared energy z_(i) of the signal y_(i) is calculated.    -   In the case of multi-channel signal, channel weighting G_(i) is        applied, and the weighted signals are summed. The loudness of        the signal is then defined to be

${L = {c + {10\;\log_{10}{\sum\limits_{i}{G_{i}z_{i}}}}}},$

-   -   with the constant value c=−0.691. The output is then expressed        in the units of “LKFS” (Loudness, K-weighted, relative to Full        Scale) which scales similarly to the decibel scale.

In the above formula, Gi may, for example, be equal to 1 for some of thechannels, while Gi may, for example, be 1.41 for some other channels.For example, if a left channel, a right channel, a center channel, aleft surround channel and a right surround channel is considered, therespective weights Gi may, for example, be 1 for the left, right andcenter channel, and may, for example, be 1.41 for the left surroundchannel and the right surround channel, see [ITU].

It can be seen, that the loudness value L is closely related to thelogarithm of the signal energy.

In the following, Spatial Audio Object Coding is described.

Object-based audio coding concepts allow for much flexibility in thedecoder side of the chain. An example of an object-based audio codingconcept is Spatial Audio Object Coding (SAOC).

FIG. 4 illustrates a Spatial Audio Object Coding (SAOC) systemcomprising an SAOC encoder 410 and an SAOC decoder 420.

The SAOC encoder 410 receives N audio object signals S1, . . . , SN asthe input. Moreover, the SAOC encoder 410 further receives instructions“Mixing information D” how these objects should be combined to obtain adownmix signal comprising M downmix channels X1, . . . , XM. The SAOCencoder 410 extracts some side information from the objects and from thedownmixing process, and this side information is transmitted and/orstored along with the downmix signals.

A major property of an SAOC system is that the downmix signal Xcomprising the downmix channels X1, . . . , XM forms a semanticallymeaningful signal. In other words, it is possible to listen to thedownmix signal. If, for example, the receiver does not have the SAOCdecoder functionality, the receiver can nonetheless provide the downmixsignal as the output.

FIG. 5 illustrates an SAOC decoder comprising a side information decoder510, an object separator 520 and a renderer 530. The SAOC decoderillustrated by FIG. 5 receives, e.g., from an SAOC encoder, the downmixsignal and the side information. The downmix signal can be considered asan audio input signal comprising the audio object signals, as the audioobject signals are mixed within the downmix signal (the audio objectsignals are mixed within the one or more downmix channels of the downmixsignal).

The SAOC decoder may, e.g., then attempt to (virtually) reconstruct theoriginal objects, e.g., by employing the object separator 520, e.g.,using the decoded side information. These (virtual) objectreconstructions Ŝ₁, . . . , Ŝ_(N), e.g., the reconstructed audio objectsignals, are then combined based on the rendering information, e.g., arendering matrix R, to produce K audio output channels Y1, . . . , YK ofan audio output signal Y.

In SAOC, often, audio object signals are, for example, reconstructed,e.g., by employing covariance information, e.g., a signal covariancematrix E, that is transmitted from the SAOC encoder to the SAOC decoder.

For example, the following formula may be employed to reconstruct theaudio object signals on the decoder side:Ŝ=GX with G≈ED ^(H)(DED ^(H))⁻¹wherein

-   -   N number of audio object signals,    -   N_(samples) number of considered samples of an audio object        signal    -   M number of downmix channels,    -   X downmix audio signal, size M×N_(Samples),    -   D downmixing matrix, size M×N    -   E signal covariance matrix, size N×N defined as E=X X^(H)    -   S parametrically reconstructed N audio object signals, size        N×N_(Samples)    -   (⋅)^(H) self-adjoint (Hermitian) operator which represents the        conjugate transpose of (⋅)

Then, a rendering matrix R may be applied on the reconstructed audioobject signals Ŝ to obtain the audio output channels of the audio outputsignal Y, e.g., according to the formula:Y=RŜwherein

-   -   K number of the audio output channels Y₁, . . . , Y_(K) of the        audio output signal Y.    -   R rendering matrix of size K×N    -   Y audio output signal comprising the K audio output channels,        size K×N_(Samples)

In FIG. 5, the process of object reconstruction, e.g., conducted by theobject separator 520, is referred to with the notion “virtual”, or“optional”, as it may not necessarily need to take place, but thedesired functionality can be obtained by combining the reconstructionand the rendering steps in the parametric domain (i.e., combining theequations).

In other words, instead of reconstructing the audio object signals usingthe mixing information D and the covariance information E first, andthen applying the rendering information R on the reconstructed audioobject signals to obtain the audio output channels Y1, . . . , YK, bothsteps may be conducted in a single step, so that the audio outputchannels Y1, . . . , YK are directly generated from the downmixchannels.

For example, the following formula may be employed:Y=RGX with G≈ED ^(H)(DED ^(H))⁻¹.

In principle, the rendering information R may request any combination ofthe original audio object signals. In practice, however, the objectreconstructions may comprise reconstruction errors and the requestedoutput scene may not necessarily be reached. As a rough general rulecovering many practical cases, the more the requested output scenediffers from the downmix signal, the more there will be audiblereconstruction errors.

In the following, dialogue enhancement (DE) is described. The SAOCtechnology may for example by employed to realize the scenario. Itshould be noted, that even though the name “Dialogue enhancement”suggests focusing on dialogue-oriented signals, the same principle canbe used with other signal types, too.

In the DE-scenario, the degrees of freedom in the system are limitedfrom the general case.

For example, the audio object signals S₁, . . . , S_(N)=S are grouped(and possibly mixed) into two meta-objects of a foreground object (FGO)S_(FGO) and a background object (BGO) S_(BGO).

Moreover, the output scene Y₁, . . . Y_(K)=Y resembles the downmixsignal X₁, . . . , X_(M)=X. More specifically, both signals have thesame dimensionalities, i.e., K=M, and the end-user can only control therelative mixing levels of the two meta-objects FGO and BGO. To be moreexact, the downmix signal is obtained by mixing the FGO and BGO withsome scalar weightsX=h _(FGO) S _(FGO) +h _(BGO) S _(BGO),and the output scene is obtained similarly with some scalar weighting ofthe FGO and BGO:Y=g _(FGO) S _(FGO) +g _(BGO) S _(BGO)Depending on the relative values of the mixing weights, the balancebetween the FGO and BGO may change. For example, with the setting

$\quad\{ \begin{matrix}{g_{FGO} > h_{FGO}} \\{g_{BGO} = h_{BGO}}\end{matrix} $it is possible to increase the relative level of the FGO in the mixture.If the FGO is the dialogue, this setting provides dialogue enhancementfunctionality.

As a use-case example, the BGO can be the stadium noises and otherbackground sound during a sports event and the FGO is the voice of thecommentator. The DE-functionality allows the end-user to amplify orattenuate the level of the commentator in relation to the background.

Embodiments are based on the finding that utilizing the SAOC-technology(or similar) in a broadcast scenario allows providing the end-userextended signal manipulation functionality. More functionality than onlychanging the channel and adjusting the playback volume is provided.

One possibility to employ the DE-technology is briefly described above.If the broadcast signal, being the downmix signal for SAOC, isnormalized in level, e.g., according to R128, the different programshave similar average loudness when no (SAOC-) processing is applied (orthe rendering description is the same as the downmixing description).However, when some (SAOC-)processing is applied, the output signaldiffers from the default downmix signal and the loudness of the outputsignal may be different from the loudness of the default downmix signal.From the point of view of the end-user, this may lead into a situationin which the output signal loudness between channels or programs mayagain have the un-desirable jumps or differences. In other words, thebenefits of the normalization applied by the broadcaster are partiallylost.

This problem is not specific for SAOC or for the DE-scenario only, butmay occur also with other audio coding concepts that allow the end-userto interact with the content. However, in many cases it does not causeany harm if the output signal has a different loudness than the defaultdownmix.

As stated before, a total loudness of an audio input signal programshould equal a specified level with small allowed deviations. However,as already outlined, this leads to significant problems when audiorendering is conducted, as rendering may have a significant effect onthe overall/total loudness of the received audio input signal. However,despite scene rendering is conducted, the total loudness of the receivedaudio signal shall remain the same.

One approach would be to estimate the loudness of a signal while it isbeing played, and with an appropriate temporal integration concept, theestimate may converge to the true average loudness after some time. Thetime necessitated for the convergence is however problematic from thepoint of view of the end-user. When the loudness estimate changes evenwhen no changes are applied on the signal, the loudness changecompensation should also react and change its behavior. This would leadinto an output signal with temporally varying average loudness, whichcan be perceived as rather annoying.

FIG. 6 illustrates a behavior of output signal loudness estimates on aloudness change. Inter alia, a signal-based output signal loudnessestimate is depicted, which illustrates the effect of a solution as justdescribed. The estimate approaches the correct estimate quite slowly.Instead of a signal-based output signal loudness estimate, an informedoutput signal loudness estimate, that immediately determines the outputsignal loudness correctly would be of advantage.

In particular, in FIG. 6, the user input, e.g., the level of thedialogue object, changes at time instant T by increasing in value. Thetrue output signal level, and correspondingly the loudness, changes atthe same time instant. When the output signal loudness estimation isperformed from the output signal with some temporal integration time,the estimate will change gradually and reach the correct value after acertain delay. During this delay, the estimate values are changing andcannot reliably be used for further processing the output signal, e.g.,for loudness level correction.

As already stated, it would be desirable to have an accurate estimate ofthe output average loudness or the change in the average loudnesswithout a delay and when the program does not change or the renderingscene is not changed, the average loudness estimate should also remainstatic. In other words, when some loudness change compensation isapplied, the compensation parameter should change only when either theprogram changes or there is some user interaction.

The desired behavior is illustrated in the lowest illustration of FIG. 6(informed output signal loudness estimate). The estimate of the outputsignal loudness shall change immediately when the user input changes.

FIG. 2 illustrates an encoder according to an embodiment.

The encoder comprises an object-based encoding unit 210 for encoding aplurality of audio object signals to obtain an encoded audio signalcomprising the plurality of audio object signals.

Furthermore, the encoder comprises an object loudness encoding unit 220for encoding loudness information on the audio object signals. Theloudness information comprises one or more loudness values, wherein eachof the one or more loudness values depends on one or more of the audioobject signals.

According to an embodiment, each of the audio object signals of theencoded audio signal is assigned to exactly one group of two or moregroups, wherein each of the two or more groups comprises one or more ofthe audio object signals of the encoded audio signal. The objectloudness encoding unit 220 is configured to determine the one or moreloudness values of the loudness information by determining a loudnessvalue for each group of the two or more groups, wherein said loudnessvalue of said group indicates an original total loudness of the one ormore audio object signals of said group.

FIG. 1 illustrates a decoder for generating an audio output signalcomprising one or more audio output channels according to an embodiment.

The decoder comprises a receiving interface 110 for receiving an audioinput signal comprising a plurality of audio object signals, forreceiving loudness information on the audio object signals, and forreceiving rendering information indicating whether one or more of theaudio object signals shall be amplified or attenuated.

Moreover, the decoder comprises a signal processor 120 for generatingthe one or more audio output channels of the audio output signal. Thesignal processor 120 is configured to determine a loudness compensationvalue depending on the loudness information and depending on therendering information. Furthermore, the signal processor 120 isconfigured to generate the one or more audio output channels of theaudio output signal from the audio input signal depending on therendering information and depending on the loudness compensation value.

According to an embodiment, the signal processor 110 is configured togenerate the one or more audio output channels of the audio outputsignal from the audio input signal depending on the renderinginformation and depending on the loudness compensation value, such thata loudness of the audio output signal is equal to a loudness of theaudio input signal, or such that the loudness of the audio output signalis closer to the loudness of the audio input signal than a loudness of amodified audio signal that would result from modifying the audio inputsignal by amplifying or attenuating the audio object signals of theaudio input signal according to the rendering information.

According to another embodiment, each of the audio object signals of theaudio input signal is assigned to exactly one group of two or moregroups, wherein each of the two or more groups comprises one or more ofthe audio object signals of the audio input signal.

In such an embodiment, the receiving interface 110 is configured toreceive a loudness value for each group of the two or more groups as theloudness information, wherein said loudness value indicates an originaltotal loudness of the one or more audio object signals of said group.Furthermore, the receiving interface 110 is configured to receive therendering information indicating for at least one group of the two ormore groups whether the one or more audio object signals of said groupshall be amplified or attenuated by indicating a modified total loudnessof the one or more audio object signals of said group. Moreover, in suchan embodiment, the signal processor 120 is configured to determine theloudness compensation value depending on the modified total loudness ofeach of said at least one group of the two or more groups and dependingon the original total loudness of each of the two or more groups.Furthermore, the signal processor 120 is configured to generate the oneor more audio output channels of the audio output signal from the audioinput signal depending on the modified total loudness of each of said atleast one group of the two or more groups and depending on the loudnesscompensation value.

In particular embodiments, at least one group of the two or more groupscomprises two or more of the audio object signals.

A direct relationship exists between the energy ei of an audio objectsignal i and the loudness Li of the audio object signal i according tothe formulae:L _(i) =c+10 log₁₀ e _(i) , e _(i)=10^((L) ^(i) ^(−c)/)10wherein c is a constant value.

Embodiments are based on the following findings: Different audio objectsignals of the audio input signal may have a different loudness and thusa different energy. If, e.g, a user wants to increase the loudness ofone of the audio object signals, the rendering information may becorrespondingly adjusted, and the increase of the loudness of this audioobject signal increases the energy of this audio object. This would leadto an increased loudness of the audio output signal. To keep the totalloudness constant, a loudness compensation has to be conducted. In otherwords, the modified audio signal that would result from applying therendering information on the audio input signal would have to beadjusted. However, the exact effect of the amplification of one of theaudio object signals on the total loudness of the modified audio signaldepends on the original loudness of the amplified audio object signal,e.g., of the audio object signal, the loudness of which is increased. Ifthe original loudness of this object corresponds to an energy, that wasquite low, the effect on the total loudness of the audio input signalwill be minor. If, however, the original loudness of this objectcorresponds to an energy, that was quite high, the effect on the totalloudness of the audio input signal will be significant.

Two examples may be considered. In both examples, an audio input signalcomprises two audio object signal, and in both examples, by applying therendering information, the energy of a first one of the audio objectsignals is increased by 50%.

In the first example, the first audio object signal contributes 20% andthe second audio object signal contributes 80% to the total energy ofthe audio input signal. However, in the second example, the first audioobject, the first audio object signal contributes 40% and the secondaudio object signal contributes 60% to the total energy of the audioinput signal. In both examples these contributions are derivable fromthe loudness information on the audio object signals, as a directrelationship exists between loudness and energy.

In the first example, an increase of 50% of the energy of the firstaudio object results in that a modified audio signal that is generatedby applying the rendering information on the audio input signal has atotal energy 1.5×20%+80%=110% of the energy of the audio input signal.

In the second example, an increase of 50% of the energy of the firstaudio object results in that the modified audio signal that is generatedby applying the rendering information on the audio input signal has atotal energy 1.5×40%+60%=120% of the energy of the audio input signal.

Thus, after applying the rendering information on the audio inputsignal, in the first example, the total energy of the modified audiosignal has to be reduced by only 9% (10/110) to obtain equal energy inboth the audio input signal and the audio output signal, while in thesecond example, the total energy of the modified audio signal has to bereduced by 17% (20/120). For this purpose, a loudness compensation valuemay be calculated.

For example, the loudness compensation value may be a scalar that isapplied on all audio output channels of the audio output signal.

According to an embodiment, the signal processor is configured togenerate the modified audio signal by modifying the audio input signalby amplifying or attenuating the audio object signals of the audio inputsignal according to the rendering information. Moreover, the signalprocessor is configured to generate the audio output signal by applyingthe loudness compensation value on the modified audio signal, such thatthe loudness of the audio output signal is equal to the loudness of theaudio input signal, or such that the loudness of the audio output signalis closer to the loudness of the audio input signal than the loudness ofthe modified audio signal.

For example, in the first example above, the loudness compensation value/cv, may, for example, be set to a value /cv=10/11, and a multiplicationfactor of 10/11 may be applied on all channels that result fromrendering the audio input channels according to the renderinginformation.

Accordingly, for example, in the second example above, the loudnesscompensation value /cv, may, for example, be set to a value/cv=10/12=5/6, and a multiplication factor of 5/6 may be applied on allchannels that result from rendering the audio input channels accordingto the rendering information.

In other embodiments, each of the audio object signals may be assignedto one of a plurality of groups, and a loudness value may be transmittedfor each of the groups indicating a total loudness value of the audioobject signals of said group. If the rendering information specifiesthat the energy of one of the groups is attenuated or amplified, e.g.,amplified by 50% as above, a total energy increase may be calculated anda loudness compensation value may be determined as described above.

For example, according to an embodiment, each of the audio objectsignals of the audio input signal is assigned to exactly one group ofexactly two groups as the two or more groups. Each of the audio objectsignals of the audio input signal is either assigned to a foregroundobject group of the exactly two groups or to a background object groupof the exactly to groups. The receiving interface 110 is configured toreceive the original total loudness of the one or more audio objectsignals of the foreground object group. Moreover, the receivinginterface 110 is configured to receive the original total loudness ofthe one or more audio object signals of the background object group.Furthermore, the receiving interface 110 is configured to receive therendering information indicating for at least one group of the exactlytwo groups whether the one or more audio object signals of each of saidat least one group shall be amplified or attenuated by indicating amodified total loudness of the one or more audio object signals of saidgroup.

In such an embodiment, the signal processor 120 is configured todetermine the loudness compensation value depending on the modifiedtotal loudness of each of said at least one group, depending on theoriginal total loudness of the one or more audio object signals of theforeground object group, and depending on the original total loudness ofthe one or more audio object signals of the background object group.Moreover, the signal processor 120 is configured to generate the one ormore audio output channels of the audio output signal from the audioinput signal depending on the modified total loudness of each of said atleast one group and depending on the loudness compensation value.

According to some embodiments, each of the audio object signals isassigned to one of three or more groups, and the receiving interface maybe configured to receive a loudness value for each of the three or moregroups indicating the total loudness of the audio object signals of saidgroup.

According to an embodiment, to determine the total loudness value of twoor more audio object signals, for example, the energy valuecorresponding to the loudness value is determined for each audio objectsignal, the energy values of all loudness values are summed up to obtainan energy sum, and the loudness value corresponding to the energy sum isdetermined as the total loudness value of the two or more audio objectsignals. For example, the formulaeL _(i) =c+10 log₁₀ e _(i) , e _(i)=10^((L) ^(i) ^(−c)/)10may be employed.

In some embodiments, loudness values are transmitted for each of theaudio object signals, or each of the audio object signals is assigned toone or two or more groups, wherein for each of the groups, a loudnessvalue is transmitted.

However, in some embodiments, for one or more audio object signals orfor one or more of the groups comprising audio object signals, noloudness value is transmitted. Instead, the decoder may, for example,assume that these audio object signals or groups of audio objectsignals, for which no loudness value is transmitted, have a predefinedloudness value. The decoder may, e.g., base all further determinationson this predefined loudness value.

According to an embodiment, the receiving interface 110 is configured toreceive a downmix signal comprising one or more downmix channels as theaudio input signal, wherein the one or more downmix channels comprisethe audio object signals, and wherein the number of the audio objectsignals is smaller than the number of the one or more downmix channels.The receiving interface 110 is configured to receive downmix informationindicating how the audio object signals are mixed within the one or moredownmix channels. Moreover, the signal processor 120 is configured togenerate the one or more audio output channels of the audio outputsignal from the audio input signal depending on the downmix information,depending on the rendering information and depending on the loudnesscompensation value. In a particular embodiment, the signal processor 120may, for example, be configured to calculate the loudness compensationvalue depending on the downmix information.

For example, the downmix information may be a downmix matrix. Inembodiments, the decoder may be an SAOC decoder. In such embodiments,the receiving interface 110 may, e.g., be further configured to receivecovariance information, e.g., a covariance matrix as described above.

With respect to the rendering information indicating whether one or moreof the audio object signals shall be amplified or attenuated, it shouldbe noted that for example, information that indicates how one or more ofthe audio object signals shall be amplified or attenuated, is renderinginformation. For example, a rendering matrix R, e.g., a rendering matrixof SAOC, is rendering information.

FIG. 3 illustrates a system according to an embodiment.

The system comprises an encoder 310 according to one of theabove-described embodiments for encoding a plurality of audio objectsignals to obtain an encoded audio signal comprising the plurality ofaudio object signals.

Moreover, the system comprises a decoder 320 according to one of theabove-described embodiments for generating an audio output signalcomprising one or more audio output channels. The decoder is configuredto receive the encoded audio signal as an audio input signal and theloudness information. Moreover, the decoder 320 is configured to furtherreceive rendering information. Furthermore, the decoder 320 isconfigured to determine a loudness compensation value depending on theloudness information and depending on the rendering information.Moreover, the decoder 320 is configured to generate the one or moreaudio output channels of the audio output signal from the audio inputsignal depending on the rendering information and depending on theloudness compensation value.

FIG. 7 illustrates informed loudness estimation according to anembodiment. On the left of transport stream 730, components of anobject-based audio coding encoder are illustrated. In particular, anobject-based encoding unit 710 (“object-based audio encoder”) and anobject loudness encoding unit 720 is illustrated (“object loudnessestimation”).

The transport stream 730 itself comprises loudness information L,downmixing information D and the output of the object-based audioencoder 710 B.

On the right of transport stream 730, components of a signal processorof an object-based audio coding decoder are illustrated. The receivinginterface of the decoder is not illustrated. An output loudnessestimator 740 and an object-based audio decoding unit 750 is depicted.The output loudness estimator 740 may be configured to determine theloudness compensation value. The object-based audio decoding unit 750may be configured to determine a modified audio signal from an audiosignal, being input to the decoder, by applying the renderinginformation R. Applying the loudness compensation value on the modifiedaudio signal to compensate a total loudness change caused by therendering is not shown in FIG. 7.

The input to the encoder consists of the input objects S in the minimum.The system estimates the loudness of each object (or some otherloudness-related information, such as the object energies), e.g., by theobject loudness encoding unit 720, and this information L is transmittedand/or stored. (It is also possible, the loudness of the objects isprovided as an input to the system, and the estimation step within thesystem can be omitted).

In the embodiment of FIG. 7, the decoder receives at least the objectloudness information and, e.g., the rendering information R describingthe mixing of the objects into the output signal. Based on these, e.g.,the output loudness estimator 740, estimates the loudness of the outputsignal and provides this information as its output.

The downmixing information D may be provided as the renderinginformation, in which case the loudness estimation provides an estimateof the downmix signal loudness. It is also possible to provide thedownmixing information as an input to the object loudness estimation,and to transmit and/or store it along the object loudness information.The output loudness estimation can then estimate simultaneously theloudness of the downmix signal and the rendered output and provide thesetwo values or their difference as the output loudness information. Thedifference value (or its inverse) describes the necessitatedcompensation that should be applied on the rendered output signal formaking its loudness similar to the loudness of the downmix signal. Theobject loudness information can additionally include informationregarding the correlation coefficients between various objects and thiscorrelation information can be used in the output loudness estimationfor a more accurate estimate.

In the following, an embodiment for dialogue enhancement application isdescribed.

In the dialogue enhancement application, as described above, the inputaudio object signals are grouped and partially downmixed to form twometa-objects, FGO and BGO, which can then be trivially summed forobtaining the final downmix signal.

Following the description of SAOC [SAOC], N input object signals arerepresented as a matrix S of the size N×NSamples, and the downmixinginformation as a matrix D of the size M×N. The downmix signals can thenbe obtained as X=DS.

The downmixing information D can now be divided into two partsD=D _(FGO) +D _(BGO)for the meta-objects.

As each column of the matrix D corresponds to an original audio objectsignal, the two component downmix matrices can be obtained by settingthe columns, which correspond to the other meta-object into zero(assuming that no original object may be present in both meta-objects).In other words, the columns corresponding to the meta-object BGO are setto zero in D_(FGO) and vice versa.

These new downmixing matrices describe the way the two meta-objects canbe obtained from the input objects, namely:S _(FGO) =D _(FGO) S and S _(BGO) =D _(BGO) S,and the actual downmixing is simplified toX=S _(FGO) +S _(BGO).

It can be also considered that the object (e.g., SAOC) decoder attemptsto reconstruct the meta-objects:{tilde over (S)} _(FGO) ≈S _(FGO) and {tilde over (S)} _(BGO) ≈S _(BGO)and the DE-specific rendering can be written as a combination of thesetwo meta-object reconstructions:Y=g _(FGO) S _(FGO) +g _(BGO) S _(BGO) ≈g _(FGO) {tilde over (S)} _(FGO)+g _(BGO) {tilde over (S)} _(BGO).

The object loudness estimation receives the two meta-objects S_(FGO) andS_(BGO) as the input and estimates the loudness of each of them: L_(FGO)being the (total/overall) loudness of S_(FGO), and L_(BGO) being the(total/overall) loudness of S_(BGO). These loudness values aretransmitted and/or stored.

As an alternative, using one of the meta-objects, e.g., the FGO, asreference, it is possible to calculate the loudness difference of thesetwo objects, e.g., asΔL _(FGO) =L _(BGO) −L _(FGO).This single value is then transmitted and/or stored.

FIG. 8 illustrates an encoder according to another embodiment. Theencoder of FIG. 8 comprises an object downmixer 811 and an object sideinformation estimator 812. Furthermore, the encoder of FIG. 8 furthercomprises an object loudness encoding unit 820. Moreover, the encoder ofFIG. 8 comprises a meta audio object mixer 805.

The encoder of FIG. 8 uses intermediate audio meta-objects as an inputto the object loudness estimation. In embodiments, the encoder of FIG. 8may be configured to generate two audio meta-objects. In otherembodiments, the encoder of FIG. 8 may be configured to generate threeor more audio meta-objects.

Inter alia, the provided concepts provide the new feature that theencoder may, e.g., estimates the average loudness of all input objects.The objects may, e.g., be mixed into a downmix signal that istransmitted. The provided concepts moreover provide the new feature thatthe object loudness and the downmixing information may, e.g., beincluded in the object-coding side information that is transmitted.

The decoder may, e.g., use the object-coding side information for(virtual) separation of the objects and re-combines the objects usingthe rendering information.

Furthermore, the provided concepts provide the new feature that eitherthe downmixing information can be used to estimate the loudness of thedefault downmix signal, the rendering information and the receivedobject loudness can be used for estimating the average loudness of theoutput signal, and/or the loudness change can be estimated from thesetwo values. Or, the downmixing and rendering information can be used toestimate the loudness change from the default downmix, another newfeature of the provided concepts.

Furthermore, the provided concepts provide the new feature that thedecoder output can be modified to compensate for the change in theloudness so that the average loudness of the modified signal matches theaverage loudness of the default downmix.

A specific embodiment related to SAOC-DE is illustrated in FIG. 9. Thesystem receives the input audio object signals, the downmixinginformation, and the information of the grouping of the objects tometa-objects. Based on these, the meta audio object mixer 905 forms thetwo meta-objects S_(FGO) and S_(BGO). It is possible, that the portionof the signal that is processed with SAOC, does not constitute theentire signal. For example, in a 5.1 channel configuration, SAOC may bedeployed on a sub-set of channels, like on the front channel (left,right, and center), while the other channels (left surround, rightsurround, and low-frequency effects) are routed around, (by-passing) theSAOC and delivered as such. These channels not processed by SAOC aredenoted with X_(BYPASS). The possible by-pass channels need to beprovided for the encoder for more accurate estimation of the loudnessinformation.

The by-pass channels may be handled in various ways.

For example, the by-pass channels may, e.g., form an independentmeta-object. This allows defining the rendering so that all threemeta-objects are scaled independently.

Or, for example, the by-pass channels may, e.g., be combined with one ofthe other two meta-objects. The rendering settings of that meta-objectcontrol also the by-pass channel portion. For example, in the dialogueenhancement scenario, it may be meaningful to combine the by-passchannels with the background meta-object: X_(BGO)=S_(BGO)+X_(BYPASS).

Or, for example, the by-pass channels may, e.g., be ignored.

According to embodiments, the object-based encoding unit 210 of theencoder is configured to receive the audio object signals, wherein eachof the audio object signals is assigned to exactly one of exactly twogroups, wherein each of the exactly two groups comprises one or more ofthe audio object signals. Moreover, the object-based encoding unit 210is configured to downmix the audio object signals, being comprised bythe exactly two groups, to obtain a downmix signal comprising one ormore downmix audio channels as the encoded audio signal, wherein thenumber of the one or more downmix channels is smaller than the number ofthe audio object signals being comprised by the exactly two groups. Theobject loudness encoding unit 220 is assigned to receive one or morefurther by-pass audio object signals, wherein each of the one or morefurther by-pass audio object signals is assigned to a third group,wherein each of the one or more further by-pass audio object signals isnot comprised by the first group and is not comprised by the secondgroup, wherein the object-based encoding unit 210 is configured to notdownmix the one or more further by-pass audio object signals within thedownmix signal.

In an embodiment, the object loudness encoding unit 220 is configured todetermine a first loudness value, a second loudness value and a thirdloudness value of the loudness information, the first loudness valueindicating a total loudness of the one or more audio object signals ofthe first group, the second loudness value indicating a total loudnessof the one or more audio object signals of the second group, and thethird loudness value indicating a total loudness of the one or morefurther by-pass audio object signals of the third group. In an anotherembodiment, the object loudness encoding unit 220 is configured todetermine a first loudness value and a second loudness value of theloudness information, the first loudness value indicating a totalloudness of the one or more audio object signals of the first group, andthe second loudness value indicating a total loudness of the one or moreaudio object signals of the second group and of the one or more furtherby-pass audio object signals of the third group.

According to an embodiment, the receiving interface 110 of the decoderis configured to receive the downmix signal. Moreover, the receivinginterface 110 is configured to receive one or more further by-pass audioobject signals, wherein the one or more further by-pass audio objectsignals are not mixed within the downmix signal. Furthermore, thereceiving interface 110 is configured to receive the loudnessinformation indicating information on the loudness of the audio objectsignals which are mixed within the downmix signal and indicatinginformation on the loudness of the one or more further by-pass audioobject signals which are not mixed within the downmix signal. Moreover,the signal processor 120 is configured to determine the loudnesscompensation value depending on the information on the loudness of theaudio object signals which are mixed within the downmix signal, anddepending on the information on the loudness of the one or more furtherby-pass audio object signals which are not mixed within the downmixsignal.

FIG. 9 illustrates an encoder and a decoder according to an embodimentrelated to the SAOC-DE, which comprises by-pass channels. Inter alia,the encoder of FIG. 9 comprises an SAOC encoder 902.

In the embodiment of FIG. 9, the possible combining of the by-passchannels with the other meta-objects takes place in the two “bypassinclusion” blocks 913, 914, producing the meta-objects X_(FGO) andX_(BGO) with the defined parts from the by-pass channels included.

The perceptual loudness L_(BYPASS), L_(FGO), and L_(BGO) of both ofthese meta-objects are estimated in the loudness estimation units 921,922, 923. This loudness information is then transformed into anappropriate encoding in a meta-object loudness information estimator 925and then transmitted and/or stored.

The actual SAOC en- and decoder operate as expected extracting theobject side information from the objects, creating the downmix signal X,and transmitting and/or storing the information to the decoder. Thepossible by-pass channels are transmitted and/or stored along the otherinformation to the decoder.

The SAOC-DE decoder 945 receives a gain value “Dialog gain” as auser-input. Based on this input and the received downmixing information,the SAOC decoder 945 determines the rendering information. The SAOCdecoder 945 then produces the rendered output scene as the signal Y. Inaddition to that, it produces a gain factor (and a delay value) thatshould be applied on the possible by-pass signals X_(BYPASS).

The “bypass inclusion” unit 955 receives this information along with therendered output scene and the by-pass signals and creates the fulloutput scene signal. The SAOC decoder 945 produces also a set ofmeta-object gain values, the amount of these depending on themeta-object grouping and desired loudness information form.

The gain values are provided to the mixture loudness estimator 960 whichalso receives the meta-object loudness information from the encoder.

The mixture loudness estimator 960 is then able to determine the desiredloudness information, which may include, but is not limited to, theloudness of the downmix signal, the loudness of the rendered outputscene, and/or the difference in the loudness between the downmix signaland the rendered output scene.

In some embodiments, the loudness information itself is enough, while inother embodiments, it is desirable to process the full output dependingon the determined loudness information. This processing may, forexample, be compensation of any possible difference in the loudnessbetween the downmix signal and the rendered output scene. Such aprocessing, e.g., by a loudness processing unit 970, would make sense inthe broadcast scenario, as it would reduce the changes in the perceivedsignal loudness regardless of the user interaction (setting of the input“dialog gain”).

The loudness-related processing in this specific embodiment comprisesthe a plurality of new features. Inter alia, the FGO, BGO, and thepossible by-pass channels are pre-mixed into the final channelconfiguration so that the downmixing can be done by simply adding thetwo pre-mixed signals together (e.g., downmix matrix coefficients of 1),which constitutes a new feature. Moreover, as a further new feature, theaverage loudness of the FGO and BGO are estimated, and the difference iscalculated. Furthermore, the objects are mixed into a downmix signalthat is transmitted. Moreover, as a further new feature, the loudnessdifference information is included to the side information that istransmitted. (new) Furthermore, the decoder uses the side informationfor (virtual) separation of the objects and re-combines the objectsusing the rendering information which is based on the downmixinginformation and the user input modification gain. Moreover, as anothernew feature, the decoder uses the modification gain and the transmittedloudness information for estimating the change in the average loudnessof the system output compared to the default downmix.

In the following, a formal description of embodiments is provided.

Assuming that the object loudness values behave similar to the logarithmof energy values when summing the objects, i.e., the loudness valuesmust be transformed into linear domain, added there, and finallytransformed back to the logarithmic domain. Motivating this through thedefinition of BS.1770 loudness measure will now be presented (forsimplicity, the number of channels is set to one, but the same principlecan be applied on multi-channel signals with appropriate summing overchannels).

The loudness of the i^(th) K-filtered signal z_(i) with the mean-squaredenergy e_(i) is defined asL _(i) =c+10 log₁₀ e _(i),wherein c is an offset constant. For example, c may be −0.691. From thisfollows that the energy of the signal can be determined from theloudness withe _(i)=10^((L) ^(i) ^(−c)/)10.

The energy of the sum of N uncorrelated signals

$z_{SUM} = {\sum\limits_{i = 1}^{N}z_{i}}$is then

${e_{SUM} = {{\sum\limits_{i = 1}^{N}e_{i}} = {\sum\limits_{i = 1}^{N}10^{{({L_{i} - c})}/10}}}},$and the loudness of this sum signal is then

$L_{SUM} = {{c + {10\;\log_{10}e_{SUM}}} = {c + {10\;\log_{10}{\sum\limits_{i = 1}^{N}{10^{{({L_{i} - c})}/10}.}}}}}$

If the signals are not uncorrelated, the correlation coefficientsC_(i,j) must be taken into account when approximating the energy of thesum signal as

${e_{SUM} = {\sum\limits_{i = 1}^{N}{\sum\limits_{j = 1}^{N}e_{i,j}}}},$wherein the cross-energy e_(i,j) between the i^(th) and j^(th) objectsis defined as

$\begin{matrix}{e_{i,j} = {C_{i,j}\sqrt{e_{i}e_{j}}}} \\{= {C_{i,j}\sqrt{10^{{({L_{i} - c})}/10}10^{{({L_{j} - c})}/10}}}} \\{{= {C_{i,j}\sqrt{10^{{({L_{i} + L_{j} - {2c}})}/10}}}},}\end{matrix}$wherein −1≤C_(i,j)≤1 is the correlation coefficient between the twoobjects i and j. When two objects are uncorrelated, the correlationcoefficient equals to 0, and when the two objects are identical, thecorrelation coefficient equals to 1.

Further extending the model with mixing weights g_(i) to be applied onthe signals in the mixing process, i.e.,

${z_{SUM} = {\sum\limits_{i = 1}^{N}{g_{i}z_{i}}}},$the energy of the sum signal will be

${e_{SUM} = {\sum\limits_{i = 1}^{N}{\sum\limits_{j = 1}^{N}{g_{i}g_{j}e_{i,j}}}}},$

and the loudness of the mixture signal can be obtained from this, asearlier, withL _(SUM) =c+10 log₁₀ e _(SUM)The difference between the loudness of two signals can be estimated asΔL(i,j)=L _(i) −L _(j).If the definition of loudness is now used as earlier, this can bewritten as

$\begin{matrix}{{\Delta\;{L( {i,j} )}} = {L_{i} - L_{j}}} \\{= {( {c + {10\log_{10}e_{i}}} ) - ( {c + {10\;\log_{10}e_{j}}} )}} \\{{= {10\log_{10}\frac{e_{i}}{e_{j}}}},}\end{matrix}$which can be observed to be a function of signal energies. If it is nowdesired to estimate the loudness difference between two mixtures

$z_{A} = {{\sum\limits_{i = 1}^{N}\;{g_{i}z_{i}\mspace{14mu}{and}\mspace{14mu} z_{B}}} = {\sum\limits_{i = 1}^{N}\;{h_{i}z_{i}}}}$with possibly differing mixing weights g_(i) and h_(i), this can beestimated with

$\begin{matrix}{{\Delta\;{L( {A,B} )}} = {10\;\log_{10}\frac{e_{A}}{e_{B}}}} \\{= {10\;\log_{10}\frac{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{g_{i}g_{j}e_{i,j}}}}{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{h_{i}h_{j}e_{i,j}}}}}} \\{= {10\;\log_{10}\frac{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{g_{i}g_{j}C_{i,j}\sqrt{10^{{({L_{i} + L_{j} - {2c}})}/10}}}}}{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{h_{i}h_{j}C_{i,j}\sqrt{10^{{({L_{i} + L_{j} - {2c}})}/10}}}}}}} \\{= {10\;\log_{10}{\frac{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{g_{i}g_{j}C_{i,j}\sqrt{10^{{({L_{i} + L_{j}})}/10}}}}}{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{h_{i}h_{j}C_{i,j}\sqrt{10^{{({L_{i} + L_{j}})}/10}}}}}.}}}\end{matrix}$

In the case the objects are uncorrelated (C_(i,j)=0, ∀i≠j and C_(i,j)=1,∀i=j), the difference estimate becomes

$\begin{matrix}{{\Delta\;{L( {A,B} )}} = {10\;\log_{10}\frac{\sum\limits_{i = 1}^{N}{g_{i}^{2}10^{{({L_{i} - c})}/10}}}{\sum\limits_{i = 1}^{N}{h_{i}^{2}10^{{({L_{i} - c})}/10}}}}} \\{= {10\;\log_{10}{\frac{\sum\limits_{i = 1}^{N}{g_{i}^{2}10^{L_{i}/10}}}{\sum\limits_{i = 1}^{N}{h_{i}^{2}10^{L_{i}/10}}}.}}}\end{matrix}$

In the following, differential encoding is considered.

It is possible to encode the per-object loudness values as differencesfrom the loudness of a selected reference object:K _(i) =L _(i) −L _(REF),wherein L_(REF) is the loudness of the reference object. This encodingis beneficial if no absolute loudness values are needed as the result,because it is now necessitated to transmit one value less, and theloudness difference estimation can be written as

${{\Delta\; L( {A,B} )} = {10\;\log_{10}\frac{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{g_{i}g_{j}C_{i,j}\sqrt{10^{{({K_{i} + K_{j}})}/10}}}}}{\sum\limits_{i = 1}^{N}\;{\sum\limits_{j = 1}^{N}\;{h_{i}h_{j}C_{i,j}\sqrt{10^{{({K_{i} + K_{j}})}/10}}}}}}},$or in the case of uncorrelated objects

${\Delta\; L( {A,B} )} = {10\;\log_{10}{\frac{\sum\limits_{i = 1}^{N}{g_{i}^{2}10^{K_{i}/10}}}{\sum\limits_{i = 1}^{N}{h_{i}^{2}10^{K_{i}/10}}}.}}$

In the following, a dialogue enhancement scenario is considered.

Considering again the application scenario of dialogue enhancement. Thefreedom of defining the rendering information in the decoder is limitedonly into changing the levels of the two meta-objects. Let usfurthermore assume that the two meta-objects are uncorrelated, i.e.,C_(FGO,BGO)=0. If the downmixing weights of the meta-objects are h_(FGO)and h_(BGO), and they are rendered with the gains f_(FGO) and f_(BGO),the loudness of the output relative to the default downmix is

$\begin{matrix}{{\Delta\;{L( {A,B} )}} = {10\;\log_{10}\frac{{f_{FGO}^{2}10^{{({L_{FGO} - c})}/10}} + {f_{BGO}^{2}10^{{({L_{BGO} - c})}/10}}}{{h_{FGO}^{2}10^{{({L_{FGO} - c})}/10}} + {h_{BGO}^{2}10^{{({L_{BGO} - c})}/10}}}}} \\{= {10\;\log_{10}{\frac{{f_{FGO}^{2}10^{L_{FGO}/10}} + {f_{BGO}^{2}10^{L_{BGO}/10}}}{{h_{FGO}^{2}10^{L_{FGO}/10}} + {h_{BGO}^{2}10^{L_{BGO}/10}}}.}}}\end{matrix}$This is then also the necessitated compensation if it is desired to havethe same loudness in the output as in the default downmix.

ΔL(A, B) may be considered as a loudness compensation value, that may betransmitted by the signal processor 120 of the decoder. ΔL(A, B) canalso be named as a loudness change value and thus the actualcompensation value can be an inverse value. Or is it ok to use the“loudness compensation factor” name for it, too? Thus, the loudnesscompensation value /cv mentioned earlier in this document wouldcorrespond to the value gDelta below.

For example, g_(Δ)=10^(−ΔL(A, B)/20) 1/ΔL(A, B) may be applied as amultiplication factor on each channel of a modified audio signal thatresults from applying the rendering information on the audio inputsignal. This equation for gDelta works in the linear domain. In thelogarithmic domain, the equation would be different such as 1/ΔL(A, B)and applied accordingly.

If the downmixing process is simplified such that the two meta-objectscan be mixed with unity weights for obtaining the downmix signal, i.e.,h_(FGO)=h_(BGO)=1, and now the rendering gains for these two objects aredenoted with g_(FGO) and g_(BGO). This simplifies the equation for theloudness change into

$\begin{matrix}{{\Delta\;{L( {A,B} )}} = {10\;\log_{10}\frac{{g_{FGO}^{2}10^{{({L_{FGO} - c})}/10}} + {g_{BGO}^{2}10^{{({L_{BGO} - c})}/10}}}{10^{{({L_{FGO} - c})}/10} + 10^{{({L_{BGO} - c})}/10}}}} \\{= {10\;\log_{10}{\frac{{g_{FGO}^{2}10^{L_{FGO}/10}} + {g_{BGO}^{2}10^{L_{BGO}/10}}}{10^{L_{FGO}/10} + 10^{L_{BGO}/10}}.}}}\end{matrix}$

Again, ΔL(A, B) may be considered as a loudness compensation value thatis determined by the signal processor 120.

In general, gFGO may be considered as a rendering gain for theforeground object FGO (foreground object group), and gBGO may beconsidered as a rendering gain for the background object BGO (backgroundobject group).

As mentioned earlier, it is possible to transmit loudness differencesinstead of absolute loudness. Let us define the reference loudness asthe loudness of the FGO meta-object L_(REF=)L_(FGO), i.e.,K_(FGO)=L_(FGO)−L_(REF)=0 and K_(BGO)=L_(BGO)−L_(REF)=L_(BGO)−L_(FGO).Now, the loudness change is

${\Delta\;{L( {A,B} )}} = {10\;\log_{10}{\frac{g_{FGO}^{2} + {g_{BGO}^{2}10^{K_{BGO}/10}}}{1 + 10^{K_{BGO}/10}}.}}$

It may also be, as the case in the SAOC-DE is, that two meta-objects donot have individual scaling factors, but one of the objects is leftun-modified, while the other is attenuated to obtain the correct mixingratio between the objects. In this rendering setting, the output will belower in loudness than the default mixture, and the change in theloudness is

${{\Delta\;{L( {A,B} )}} = {10\;\log_{10}\frac{{\hat{g}}_{FGO}^{2} + {{\hat{g}}_{BGO}^{2}10^{K_{BGO}/10}}}{1 + 10^{K_{BGO}/10}}}},$with

${\hat{g}}_{FGO} = \{ {\begin{matrix}{1,} & {{{if}\mspace{14mu} g_{FGO}} \geq g_{BGO}} \\{\frac{g_{FGO}}{g_{BGO}},} & {{{if}\mspace{14mu} g_{FGO}} < g_{BGO}}\end{matrix},{{{and}\mspace{14mu}{\hat{g}}_{BGO}} = \{ {\begin{matrix}{\frac{g_{BGO}}{g_{FGO}},} & {{{if}\mspace{14mu} g_{BGO}} < g_{FGO}} \\{1,} & {{{if}\mspace{14mu} g_{BGO}} \geq g_{FGO}}\end{matrix}.} }} $

This form is already rather simple, and is rather agnostic regarding theloudness measure used. The only real requirement is, that the loudnessvalues should sum in the exponential domain. It is possible totransmit/store values of signal energies instead of loudness values, asthe two have close connection.

In each of the above formulae, ΔL(A, B) may be considered as a loudnesscompensation value that may be transmitted by the signal processor 120of the decoder.

In the following, example cases are considered. The accuracy of theprovided concepts is illustrated through two example signals. Bothsignals have a 5.1 downmix with the surround and LFE channels by-passedfrom the SAOC processing.

Two main approaches are used: one (“3-term”) with three meta-objects:FGO, BGO, and by-pass channels, e.g.,X=X _(FGO) +X _(BGO) +X _(BYPASS),And another one (“2-term”) with two meta-objects, e.g.:X=X _(FGO) +X _(BGO)In the 2-term approach, the by-pass channels may, e.g., be mixedtogether with the BGO for the meta-object loudness estimation. Theloudness of both (or all three) objects as well as the loudness of thedownmix signal are estimated, and the values are stored.

The rendering instructions are of formY=ĝ _(FGO) X _(FGO) +ĝ _(BGO) X _(BGO) +ĝ _(BGO) X _(BYPASS)andY=ĝ _(FGO) X _(FGO) +ĝ _(BGO) X _(BGO)for the two approaches respectively.

The gain values are, e.g., determined according to:

${\hat{g}}_{FGO} = \{ {\begin{matrix}{1,} & {{{if}\mspace{14mu} g_{FGO}} > 1} \\{g_{FGO},} & {otherwise}\end{matrix},{{{and}\mspace{14mu}{\hat{g}}_{BGO}} = \{ {\begin{matrix}{\frac{1}{g_{FGO}},} & {{{if}\mspace{14mu} g_{FGO}} > 1} \\{1,} & {otherwise}\end{matrix},} }} $wherein the FGO gain g_(FGO) is varied between −24 to +24 dB.

The output scenario is rendered, the loudness is measured, and theattenuation from the loudness of the downmix signal is calculated.

This result is displayed in FIG. 10 and FIG. 11 with the blue line withcircle markers. FIG. 10 depicts a first illustration and FIG. 11 depictsa second illustration of a measured loudness change and the result ofusing the provided concepts for estimating the change in the loudness ina purely parametrical manner.

Next, the attenuation from the downmix is estimated parametricallyemploying the stored meta-object loudness values and the downmixing andrendering information. The estimate using the loudness of threemeta-objects is illustrated with the green line with square markers, andthe estimate using the loudness of two meta-objects is illustrated withthe red line with star markers.

It can be seen from the figures, that the 2- and 3-term approachesprovide practically identical results, and they both approximate themeasured value quite well.

The provided concepts exhibit a plurality of advantages. For example,the provided concepts allow estimating the loudness of a mixture signalfrom the loudness of the component signals forming the mixture. Thebenefit of this is that the component signal loudness can be estimatedonce, and the loudness estimate of the mixture signal can be obtainedparametrically for any mixture without the need of actual signal-basedloudness estimation. This provides a considerable improvement in thecomputational efficiency of the overall system in which the loudnessestimate of various mixtures is needed. For example, when the end-userchanges the rendering settings, the loudness estimate of the output isimmediately available.

In some applications, such as when conforming with the EBU R128recommendation, the average loudness over the entire program isimportant. If the loudness estimation in the receiver, e.g., in abroadcast scenario, is done based on the received signal, the estimateconverges to the average loudness only after the entire program has beenreceived. Because of this, any compensation of the loudness will haveerrors or exhibit temporal variations. When estimating the loudness ofthe component objects as proposed and transmitting the loudnessinformation, it is possible to estimate the average mixture loudness inthe receiver without a delay.

If it is desired that the average loudness of the output signal remains(approximately) constant regardless of the changes in the renderinginformation, the provided concepts allow determining a compensationfactor for this reason. The calculations needed for this in the decoderare from their computational complexity negligible, and thefunctionality is thus possible to be added to any decoder.

There are cases in which the absolute loudness level of the output isnot important, but the importance lies in determining the change in theloudness from a reference scene. In such cases the absolute levels ofthe objects are not important, but their relative levels are. Thisallows defining one of the objects as the reference object andrepresenting the loudness of the other objects in relation to theloudness of this reference object. This has some benefits consideringthe transport and/or storage of the loudness information.

First of all, it is not necessary to transport the reference loudnesslevel. In the application case of two meta-objects, this halves theamount of data to be transmitted. The second benefit relates to thepossible quantization and representation of the loudness values. Sincethe absolute levels of the objects can be almost anything, the absoluteloudness values can also be almost anything. The relative loudnessvalues, on the other hand, are assumed to have a 0 mean and a rathernicely formed distribution around the mean. The difference between therepresentations allows defining the quantization grid of the relativerepresentation in a way with potentially greater accuracy with the samenumber of bits used for the quantized representation.

FIG. 12 illustrates another embodiment for conducting loudnesscompensation. In FIG. 12, loudness compensation may be conducted, e.g.,to compensate the loss in loudness, For this purpose, e.g., the valuesDE_loudness_diff_dialogue (=KFGO) and DE_loudness_diff_background(=KBGO) from —_control_info may be used. Here, DE_control_info mayspecify Advanced Clean Audio “Dialogue Enhancement” (DE) controlinformation

The loudness compensation is achieved by applying a gain value “g” onthe SAOC-DE output signal and the by-passed channels (in case of amultichannel signal).

In the embodiment of FIG. 12, this is done as follows:

A limited dialogue modification gain value m_(G) is used to determinethe effective gains for the foreground object (FGO, e.g., dialogue) andfor the background object (BGO, e.g., ambiance). This is done by the“Gain mapping” block 1220 which produces the gain values m_(FGO) andm_(BGO).

The “Output loudness estimator” block 1230 uses the loudness informationK_(FGO) and K_(BGO), and the effective gain values m_(FGO) and m_(BGO)to estimate this possible change in the loudness compared to the defaultdownmix case. The change is then mapped into the “Loudness compensationfactor” which is applied on the output channels for producing the final“Output signals”.

The following steps are applied for loudness compensation:

-   -   Receive the limited gain value m_(G) from the SAOC-DE decoder        (as defined in clause 12.8 “Modification range control for        SAOC-DE” [DE]), and determine the applied FGO/BGO gains:

$\{ {\begin{matrix}{{m_{FGO} = m_{G}},{{{and}\mspace{14mu} m_{BGO}} = 1}} & {{{if}\mspace{14mu} m_{G}} \leq 1} \\{{m_{FGO} = 1},{{{and}\mspace{14mu} m_{BGO}} = m_{G}^{- 1}}} & {{{if}\mspace{14mu} m_{G}} > 1}\end{matrix}.} $

-   -   Obtain the meta-object loudness information K_(FGO) and K_(BGO).    -   Calculate the change in the output loudness compared to the        default downmix with

${\Delta\; L} = {10\;\log_{10}{\frac{{m_{FGO}^{2}10^{K_{{FGO}/10}}} + {m_{BGO}^{2}10^{K_{{BGO}/10}}}}{10^{K_{{FGO}/10}} + 10^{K_{{BGO}/10}}}.}}$

-   -   Calculate the loudness compensation gain g_(Δ)=10^(−0.05ΔL).    -   Calculate the scaling factors

${g = \begin{bmatrix}g_{1} \\\vdots \\g_{N}\end{bmatrix}},$wherein

$g_{i} = \{ \begin{matrix}g_{\Delta} \\{m_{BGO}g_{\Delta}}\end{matrix} $if channel i belongs to SAOC-DE output, if channel i is a by-passchannel and N is the total number of output channels. In FIG. 12, thegain adjustment is divided into two steps: the gain of the possible“by-pass channels” is adjusted with m_(BGO) prior to combining them withthe “SAOC-DE output channels”, and then a common gain g_(Δ) is thenapplied on all the combined channels. This is only a possiblere-ordering of the gain adjustment operations, while g here combinesboth gain adjustment steps into one gain adjustment.

-   -   Apply the scaling values g on the audio channels Y_(FULL)        consisting of the “SAOC-DE output channels” Y_(SAOC) and the        possible time-aligned “by-pass channels” Y_(BYPASS):        Y_(FULL)=Y_(SAOC)∪Y_(BYPASS).

Applying the scaling values g on the audio channels Y_(FULL) isconducted by the gain adjustment unit 1240.

ΔL as calculated above may be considered as a loudness compensationvalue. In general, mFGO indicates a rendering gain for the foregroundobject FGO (foreground object group), and mBGO indicates a renderinggain for the background object BGO (background object group).

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus.

The inventive decomposed signal can be stored on a digital storagemedium or can be transmitted on a transmission medium such as a wirelesstransmission medium or a wired transmission medium such as the Internet.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a CD, a ROM, a PROM, an EPROM, an EEPROMor a FLASH memory, having electronically readable control signals storedthereon, which cooperate (or are capable of cooperating) with aprogrammable computer system such that the respective method isperformed.

Some embodiments according to the invention comprise a non-transitorydata carrier having electronically readable control signals, which arecapable of cooperating with a programmable computer system, such thatone of the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods may be performed by any hardware apparatus.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which will beapparent to others skilled in the art and which fall within the scope ofthis invention. It should also be noted that there are many alternativeways of implementing the methods and compositions of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

REFERENCES

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The invention claimed is:
 1. A decoder for generating an audio outputsignal comprising one or more audio output channels, wherein the decodercomprises: a receiving interface for receiving an audio input signalcomprising a plurality of audio object signals, and for receivingrendering information indicating whether one or more of the audio objectsignals shall be amplified or attenuated, and a signal processor forgenerating the one or more audio output channels of the audio outputsignal, wherein the receiving interface is configured to receive adownmix signal comprising one or more downmix channels as the audioinput signal, wherein the one or more downmix channels comprise theaudio object signals, and wherein the number of the one or more downmixchannels is smaller than the number of the audio object signals, whereinthe receiving interface is configured to receive downmix informationindicating how the audio object signals are mixed within the one or moredownmix channels, wherein the signal processor is configured tocalculate a loudness compensation value depending on the information onthe loudness of each of the audio object signals which are mixed withinthe downmix signal and depending on information on a loudness of one ormore further by-pass audio object signals not mixed within the downmixsignal, and wherein the signal processor is configured to generate theone or more audio output channels of the audio output signal from theaudio input signal depending on the downmix information, depending onthe rendering information, depending on the loudness compensation value.2. The decoder according to claim 1, wherein the signal processor isconfigured to generate the modified audio signal by modifying the audioinput signal by amplifying or attenuating the audio object signals ofthe audio input signal according to the rendering information, andwherein the signal processor is configured to generate the audio outputsignal by applying the loudness compensation value on the modified audiosignal, such that the loudness of the audio output signal is equal tothe loudness of the audio input signal, or such that the loudness of theaudio output signal is closer to the loudness of the audio input signalthan the loudness of the modified audio signal.
 3. The decoder accordingto claim 1, wherein each of the audio object signals of the audio inputsignal is assigned to exactly one group of two or more groups, whereineach of the two or more groups comprises one or more of the audio objectsignals of the audio input signal, wherein the receiving interface isconfigured to receive a loudness value for each group of the two or moregroups, wherein the signal processor is configured to determine theloudness compensation value depending on the loudness value of each ofthe two or more groups, and wherein the signal processor is configuredto generate the one or more audio output channels of the audio outputsignal from the audio input signal depending on the loudnesscompensation value.
 4. The decoder according to claim 1, wherein atleast one group of the two or more groups comprises two or more of theaudio object signals.
 5. The decoder according to claim 1, wherein eachof the audio object signals of the audio input signal is assigned toexactly one group of exactly two groups as the two or more groups,wherein each of the audio object signals of the audio input signal iseither assigned to a foreground object group of the exactly two groupsor to a background object group of the exactly two groups, wherein thereceiving interface is configured to receive the loudness value of theforeground object group, wherein the receiving interface is configuredto receive the loudness value of the background object group, whereinthe signal processor is configured to determine the loudnesscompensation value depending on the loudness value of the foregroundobject group, and depending on the loudness value of the backgroundobject group, and wherein the signal processor is configured to generatethe one or more audio output channels of the audio output signal fromthe audio input signal depending on the loudness compensation value. 6.The decoder according to claim 5, wherein the signal processor isconfigured to determine a loudness compensation value ΔL according tothe formula${\Delta\; L} = {10\log_{10}\frac{{m_{FGO}^{2}10^{K_{FGO}/10}} + {m_{BGO}^{2}10^{K_{BGO}/10}}}{10^{K_{FGO}/10} + 10^{K_{BGO}/10}}}$wherein K_(FGO) indicates the loudness value of the foreground objectgroup, wherein K_(BGO) indicates the loudness value of the backgroundobject group, wherein m_(FGO) indicates a rendering gain of theforeground object group, and wherein mBGO indicates a rendering gain ofthe background object group.
 7. The decoder according to claim 5,wherein the signal processor is configured to determine a loudnesscompensation value ΔL according to the formula${\Delta\;{L( {A,B} )}} = {10\log_{10}\frac{{g_{FGO}^{2}10^{L_{FGO}/10}} + {g_{BGO}^{2}10^{L_{BGO}/10}}}{10^{L_{FGO}/10} + 10^{L_{BGO}/10}}}$wherein L_(FGO) indicates the loudness value of the foreground objectgroup, wherein L_(BGO) indicates the loudness value of the backgroundobject group, wherein g_(FGO) indicates a rendering gain of theforeground object group, and wherein g_(BGO) indicates a rendering gainof the background object group.
 8. An encoder, comprising: anobject-based encoding unit for encoding a plurality of audio objectsignals to acquire an encoded audio signal comprising the plurality ofaudio object signals, and an object loudness encoding unit for encodingone or more loudness values, wherein each of the one or more loudnessvalues depends on one or more of the audio object signals, wherein theobject-based encoding unit is configured to receive the audio objectsignals, wherein each of the audio object signals is assigned to exactlyone of two or more groups, wherein each of the two or more groupscomprises one or more of the audio object signals, wherein theobject-based encoding unit is configured to downmix the audio objectsignals, being comprised by the two or more groups, to acquire a downmixsignal comprising one or more downmix audio channels as the encodedaudio signal, wherein the number of the one or more downmix channels issmaller than the number of the audio object signals being comprised bythe two or more groups, wherein the object loudness encoding unitassigned to receive one or more further by-pass audio object signals;wherein each of the one or more further by-pass audio object signals isassigned to a third group, wherein each of the one or more furtherby-pass audio object signals is not comprised by the first group and isnot comprised by the second group, wherein the object based encodingunit is configured to not downmix the one or more further by-pass audioobject signals within the downmix signal.
 9. The encoder according toclaim 8, wherein the two or more groups are exactly two groups, whereineach of the audio object signals is assigned to exactly one of theexactly two groups, wherein each of the exactly two groups comprises oneor more of the audio object signals, wherein the object-based encodingunit is configured to downmix the audio object signals, being comprisedby the exactly two groups, to acquire a downmix signal comprising one ormore downmix audio channels as the encoded audio signal, wherein thenumber of the one or more downmix channels is smaller than the number ofthe audio object signals being comprised by the exactly two groups. 10.A system comprising: an encoder according to claim 8 for encoding aplurality of audio object signals to acquire an encoded audio signalcomprising the plurality of audio object signals, and a decoder forgenerating an audio output signal comprising one or more audio outputchannels, wherein the decoder comprises: a receiving interface forreceiving, from the encoder, an audio input signal comprising aplurality of audio object signals, and for receiving renderinginformation indicating whether one or more of the audio object signalsshall be amplified or attenuated, and a signal processor for generatingthe one or more audio output channels of the audio output signal,wherein the receiving interface is configured to receive, from theencoder, a downmix signal comprising one or more downmix channels as theaudio input signal, wherein the one or more downmix channels comprisethe audio object signals, and wherein the number of the one or moredownmix channels is smaller than the number of the audio object signals,wherein the receiving interface is configured to receive, for theencoder, downmix information indicating how the audio object signals aremixed within the one or more downmix channels, wherein the signalprocessor is configured to calculate a loudness compensation valuedepending on each of the information on the loudness of the audio objectsignals which are mixed within the downmix signal and depending oninformation, received from the encoder, on a loudness of one or morefurther by-pass audio object signals not mixed within the downmixsignal, and wherein the signal processor is configured to generate theone or more audio output channels of the audio output signal from theaudio input signal depending on the downmix information, depending onthe rendering information and depending on the loudness compensationvalue.
 11. A method for generating an audio output signal comprising oneor more audio output channels, wherein the method comprises: receivingan audio input signal comprising a plurality of audio object signals,receiving rendering information indicating whether one or more of theaudio object signals shall be amplified or attenuated, receiving adownmix signal comprising one or more downmix channels as the audioinput signal, wherein the one or more downmix channels comprise theaudio object signals, and wherein the number of the one or more downmixchannels is smaller than the number of the audio object signals,receiving downmix information indicating how the audio object signalsare mixed within the one or more downmix channels, calculating aloudness compensation value depending on the information on the loudnessof each of the audio object signals which are mixed within the downmixsignal and depending on information on a loudness of one or more furtherby-pass audio object signals not mixed within the downmix signal, andgenerating the one or more audio output channels of the audio outputsignal from the audio input signal depending on the downmix information,depending on the rendering information and depending on the loudnesscompensation value.
 12. A non-transitory computer-readable mediumcomprising a computer program for implementing the method according toclaim 11 when being executed on a computer or signal processor.
 13. Amethod for encoding, comprising: encoding an audio input signalcomprising a plurality of audio object signals, and encoding one or moreloudness values, wherein each of the one or more loudness values dependson one or more of the audio object signals, wherein each of the audioobject signals is assigned to exactly one of two or more groups, whereineach of the two or more groups comprises one or more of the audio objectsignals, wherein encoding the one or more loudness values is conductedby downmixing the audio object signals, being comprised by the two ormore groups, to acquire a downmix signal comprising one or more downmixaudio channels as the encoded audio signal, wherein the number of theone or more downmix channels is smaller than the number of the audioobject signals being comprised by the two or more groups, wherein eachof one or more further by-pass audio object signals is assigned to athird group, wherein each of the one or more further by pass audioobject signals is not comprised by the first group and is notcompromised by the second group, wherein encoding the one or moreloudness values is conducted by now downmixing the one or more furtherby-pass audio object signals within the downmix signal.
 14. Anon-transitory computer-readable medium comprising a computer programfor implementing the method according to claim 13 when being executed ona computer or signal processor.